Achieving hearing aid compatibility on handsets with low acoustic impedance receivers

Abstract

In one embodiment, an equalizer outputs a compensated received signal that flattens the acoustic frequency response characteristic of a handset having a leak tolerant ear piece. A hardware based filter is implemented within the handset having a response matched to the response of the equalizer so that the acoustic and magnetic frequency responses of the handset are substantially flat over the audible frequency range to comply with regulatory requirements.

1. A method comprising:
 receiving an uncompensated received signal for driving a voice coil and hearing aid coil included in the receiver of a handset, with the handset having an acoustic frequency response characteristic having a drop between about 1000 and 3000 hertz and having a substantially flat magnetic frequency response characteristic over the audible frequency range when driven by the uncompensated received signal; 
 equalizing the uncompensated received signal to form a compensated received signal where the acoustic frequency response characteristic of the handset is substantially flat over the audible frequency range when driven by the compensated received signal; and 
 filtering the compensated received signal applied to the hearing aid coil so that the magnetic frequency response characteristic of the handset is substantially flat over the audible frequency range when driven by the compensated received signal. 
 
     
     
       2. The method of  claim 1  where the step of equalizing further comprises:
 digital signal processing of the received signal. 
 
     
     
       3. The method of  claim 1  where the step of filtering further comprises:
 applying the compensated received signal to a circuit comprising a capacitive element and an inductive element. 
 
     
     
       4. An apparatus comprising:
 a receiver, included in a handset having first and second handset terminals, with the receiver having VC (Voice Coil), HAC (Hearing Aid Coil), and COMMON terminals, with the VC terminal coupled to the first handset terminal and the HAC terminal coupled to the second handset terminal; 
 a voice coil, included in the receiver, having a first voice coil terminal coupled to the VC terminal and a second voice coil terminal coupled to the COMMON terminal; 
 a hearing aid coil, included in the receiver, having a first hearing aid coil terminal coupled to the COMMON terminal and second hearing aid coil terminal coupled to the HAC terminal, and 
 a filter having a first filter terminal coupled to the COMMON terminal and a second filter terminal coupled to the HAC terminal, with the filter tuned so that the magnetic frequency response of the handset is substantially flat over the audible range of frequencies when a compensated signal is coupled to the first and second handset terminals, where the acoustic frequency response of the handset to the compensated signal is substantially flat over the audible range of frequencies. 
 
     
     
       5. The apparatus of  claim 4  further comprising:
 a base unit having first and second base terminals adapted to be coupled to the first and second handset terminals: 
 an equalizer, included in the base unit, with the equalizer configured to generate a compensated signal that when applied to the voice coil causes the acoustic frequency response characteristic of the handset to be substantially flat over the audible frequency range. 
 
     
     
       6. The apparatus of  claim 4  where the equalizer is a digital signal processor. 
     
     
       7. The apparatus of  claim 4  where the filter causes the magnetic frequency response characteristic of the handset to be flat over the audible frequency range when the compensated signal is applied to the first and second handset terminals. 
     
     
       8. The apparatus of  claim 4  where the filter comprises:
 an inductive element; and 
 a capacitive element. 
 
     
     
       9. A system comprising:
 means for receiving an uncompensated received signal for driving a voice coil and hearing aid coil included in the receiver of a handset, with the handset having an acoustic frequency response characteristic having a drop between about 1000 and 3000 hertz and having a substantially flat magnetic frequency response characteristic over the audible frequency range when driven by the uncompensated received signal; 
 means for equalizing the uncompensated received signal to form a compensated received signal where the acoustic frequency response characteristic of the handset is substantially flat over the audible frequency range when driven by the compensated received signal; and 
 means for filtering the compensated received signal applied to the hearing aid coil so that the magnetic frequency response characteristic of the handset is substantially flat over the audible frequency range when driven by the compensated received signal. 
 
     
     
       10. The system of  claim 9  where the means for equalizing further comprises:
 means for digital signal processing of the received signal. 
 
     
     
       11. The system of  claim 9  where the means for filtering further comprises:
 means for applying the compensated received signal to a circuit comprising a capacitive element and an inductive element.